Electric motors having gear reduction are widely employed for many industrial applications. Typically, the gear reduction is provided by a gear train formed of at least two meshing gear members, one of which is driven by the motor output shaft and may be actually incorporated into the structure of the motor output shaft, and the second fixed on an axle or shaft thereby rotating the shaft upon rotation of the motor output shaft.
In a typical application of such a motor/gearbox drive, windshield arms and blades are attached to a conventional linkage which includes a crank arm fixedly mounted on the rotatable output shaft of a motor/gear drive. Within the motor/gearbox housing, a worm gear is formed on the motor output shaft. One end of the shaft is rotatably mounted in a bore formed in the housing. An intermediate end of the shaft is also supported in a bearing mounted in the housing.
Cost reduction in the motor/gearbox drive has focused on the worm gear shaft and related components. Cost reduction can be achieved in this area by using a smaller diameter worm gear shaft. However, without support at the end of the shaft, the gear train fails at less than the required torque output. Such failure is a result of excessive deflection of the worm gear shaft. To control the deflection of the shaft, a bearing surface is required at the end of the shaft. A thrust bearing surface is also required to control axial movement of the shaft. One solution is to machine a bore in the housing, which then receives a press-in bearing. However, the location of the machined bore cannot be held to the necessary tolerance for proper location of the bearing-to-shaft journal. Proper location of this journal is essential for low noise and high efficiency of the motor/gearbox drive. If the bearing is more than a few thousandths of an inch out of position, excessive noise and friction result.
Axial end play of the gear shaft must also be controlled by minimizing such axial movement in order to prevent noise. It is known to provide a drilled and tapped bore in the housing axially in line with the worm gear shaft, which bore receives a threaded screw carrying a molded elastomer or resilient end cap. The screw is threaded into the tapped bore a sufficient distance to bring the end cap into engagement with the shaft. While this minimizes axial movement of the shaft to a certain extent, such an arrangement introduces other problems, the most significant of which is the drilled bore which forms a new water path entry into the motor/gearbox housing. In addition, the end cap applies force to the shaft and thereby controls the gear meshing.
Another solution to the radial and axial movement problems associated with a smaller diameter worm gear shaft is to provide another bearing in the gearbox housing to support the end of the shaft. However, this introduces an added cost into the motor gearbox drive.
Thus, it would be desirable to provide a motor/gearbox drive having molded sleeve and thrust elements or bearing surfaces which enable a smaller than normal diameter output drive shaft to be employed while still preventing excess radial deflection and excess axial movement of the drive shaft. It would also be desirable to provide such thrust and sleeve elements which minimize noise during operation of the motor/gear drive. It would also be desirable to provide sleeve and thrust bearing surfaces for a motor gear drive which can be easily integrated with existing motor/gearbox production methods for low manufacturing costs.